Shuttle Radar Topography Mission
Encyclopedia
Digital elevation model
A digital elevation model is a digital model or 3-D representation of a terrain's surface — commonly for a planet , moon, or asteroid — created from terrain elevation data....
s on a near-global scale from 56° S to 60° N, to generate the most complete high-resolution digital topographic database of Earth prior to the release of the ASTER GDEM in 2009. SRTM consisted of a specially modified radar
Radar
Radar is an object-detection system which uses radio waves to determine the range, altitude, direction, or speed of objects. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain. The radar dish or antenna transmits pulses of radio...
system that flew on board the Space Shuttle
Space Shuttle
The Space Shuttle was a manned orbital rocket and spacecraft system operated by NASA on 135 missions from 1981 to 2011. The system combined rocket launch, orbital spacecraft, and re-entry spaceplane with modular add-ons...
Endeavour
Space Shuttle Endeavour
Space Shuttle Endeavour is one of the retired orbiters of the Space Shuttle program of NASA, the space agency of the United States. Endeavour was the fifth and final spaceworthy NASA space shuttle to be built, constructed as a replacement for Challenger...
during the 11-day STS-99
STS-99
STS-99 was a Space Shuttle Endeavour mission, that launched on 11 February 2000 from Kennedy Space Center, Florida. The primary objective of the mission was the Shuttle Radar Topography Mission project.-Crew:-Mission parameters:*Mass:...
mission in February 2000, based on the older Spaceborne Imaging Radar-C/X-band Synthetic Aperture Radar (SIR-C/X-SAR), previously used on the Shuttle in 1994. To acquire topographic
Topography
Topography is the study of Earth's surface shape and features or those ofplanets, moons, and asteroids...
(elevation) data, the SRTM payload was outfitted with two radar antennas. One antenna was located in the Shuttle's payload bay, the other – a critical change from the SIR-C/X-SAR, allowing single-pass interferometry – on the end of a 60-meter (200-foot) mast that extended from the payload bay once the Shuttle was in space. The technique employed is known as Interferometric Synthetic Aperture Radar
Interferometric synthetic aperture radar
Interferometric synthetic aperture radar, also abbreviated InSAR or IfSAR, is a radar technique used in geodesy and remote sensing. This geodetic method uses two or more synthetic aperture radar images to generate maps of surface deformation or digital elevation, using differences in the phase of...
.
The elevation models are arranged into tiles, each covering one degree
Degree (angle)
A degree , usually denoted by ° , is a measurement of plane angle, representing 1⁄360 of a full rotation; one degree is equivalent to π/180 radians...
of latitude and one degree of longitude, named according to their south western corners. It follows that "n45e006" stretches from 45°N 6°E
6th meridian east
The meridian 6° east of Greenwich is a line of longitude that extends from the North Pole across the Arctic Ocean, Europe, Africa, the Atlantic Ocean, the Southern Ocean, and Antarctica to the South Pole....
to 46°N
46th parallel north
The 46th parallel north is a circle of latitude that is 46 degrees north of the Earth's equatorial plane. It crosses Europe, Asia, the Pacific Ocean, North America, and the Atlantic Ocean....
7°E
7th meridian east
The meridian 7° east of Greenwich is a line of longitude that extends from the North Pole across the Arctic Ocean, Europe, Africa, the Atlantic Ocean, the Southern Ocean, and Antarctica to the South Pole....
and "s45w006" from 45°S
45th parallel south
The 45th parallel south is a circle of latitude that is 45 degrees south of the Earth's equatorial plane. It is the line that marks the theoretical halfway point between the equator and the South Pole...
6°W
6th meridian west
The meridian 6° west of Greenwich is a line of longitude that extends from the North Pole across the Arctic Ocean, the Atlantic Ocean, Europe, Africa, the Southern Ocean, and Antarctica to the South Pole....
to 44°S
44th parallel south
The 44th parallel south is a circle of latitude that is 44 degrees south of the Earth's equatorial plane. It crosses the Atlantic Ocean, the Indian Ocean, Australasia, the Pacific Ocean and South America....
5°W
5th meridian west
The meridian 5° west of Greenwich is a line of longitude that extends from the North Pole across the Arctic Ocean, the Atlantic Ocean, Europe, Africa, the Southern Ocean, and Antarctica to the South Pole....
. The resolution of the cells of the source data is one arc second, but 1" (approx. 30 meter) data have only been released over United States territory; for the rest of the world, only three-arc-second (approx. 90-meter) data are available. Each one arc second tile has 3,601 rows, each consisting of 3,601 16 bit bigendian cells. The dimensions of the three-arc-second tiles are 1201 x 1201.
The elevation models derived from the SRTM data are used in Geographic Information Systems. They can be downloaded freely over the Internet, and their file format (.hgt) is supported by several software developments.
The Shuttle Radar Topography Mission is an international project spearheaded by the U.S. National Geospatial-Intelligence Agency (NGA
National Geospatial-Intelligence Agency
The National Geospatial-Intelligence Agency is an agency of the federal government of the United States with the primary mission of collecting, analyzing and distributing geospatial intelligence in support of national security. NGA was formerly known as the National Imagery and Mapping Agency ...
) and the U.S. National Aeronautics and Space Administration (NASA
NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
).
No-data areas
The elevation datasets are affected by mountain and desert no-data areas. These amount to no more than 0.2% of the total area surveyed, but can be a problem in areas of very high relief. They affect all summits over 8,000 meters, most summits over 7,000 meters, many Alpine and similar summits and ridges, and many gorges and canyons. There are some SRTM data sources which have filled these data voids, but some of these have used only interpolationInterpolation
In the mathematical field of numerical analysis, interpolation is a method of constructing new data points within the range of a discrete set of known data points....
from surrounding data, and may therefore be very inaccurate. If the voids are large, or completely cover summit or ridge areas, no interpolation algorithms will give satisfactory results. Other developers, including NASA World Wind
NASA World Wind
World Wind is an open-source virtual globe developed by NASA and the open source community for use on personal computers. Old versions need Microsoft Windows but the more recent Java version, , is cross platform and provides a suite of . The World Wind Java version was awarded in November 2009...
and Google Earth
Google Earth
Google Earth is a virtual globe, map and geographical information program that was originally called EarthViewer 3D, and was created by Keyhole, Inc, a Central Intelligence Agency funded company acquired by Google in 2004 . It maps the Earth by the superimposition of images obtained from satellite...
, have improved their results by using 30-arc-second data in the interpolation process, but, due to the poor resolution of these data, and very poor quality of some of them, they have further improved their earth viewing services by adding data from other sources. Readers with Google Earth software can examine an example of the most recent results by clicking on 27°59′14"N 86°55′31"E (Mount Everest
Mount Everest
Mount Everest is the world's highest mountain, with a peak at above sea level. It is located in the Mahalangur section of the Himalayas. The international boundary runs across the precise summit point...
) and tilting the image.
Void-filled SRTM datasets
Groups of scientists have worked on algorithms to fill the voids of the original SRTM data. Two datasets offer global coverage void-filled SRTM data at full resolution: the CGIAR-CSI versions and the USGS HydroSHEDS dataset. The CGIAR-CSI version 4 provides the best global coverage full resolution SRTM dataset. The HydroSHEDS dataset was generated for hydrological applications and is suitable for consistent drainage and water flow information. References are provided on the algorithms used and quality assessment. The void-filled SRTM data from Viewfinder Panoramas are high quality at full SRTM resolution, but coverage is limited to areas of high mountain void incidence, and some areas north of 60 degrees of latitude.Users
In early June 2011, there were 750,000 confirmed users of SRTM topography dataset. Users in 221 countries have accessed the site (everywhere except Western SaharaWestern Sahara
Western Sahara is a disputed territory in North Africa, bordered by Morocco to the north, Algeria to the northeast, Mauritania to the east and south, and the Atlantic Ocean to the west. Its surface area amounts to . It is one of the most sparsely populated territories in the world, mainly...
.)
See also
- Advanced Spaceborne Thermal Emission and Reflection RadiometerAdvanced Spaceborne Thermal Emission and Reflection RadiometerASTER is a Japanese sensor which is one of five remote sensory devices on board the Terra satellite launched into Earth orbit by NASA in 1999...
- Interferometric Synthetic Aperture RadarInterferometric synthetic aperture radarInterferometric synthetic aperture radar, also abbreviated InSAR or IfSAR, is a radar technique used in geodesy and remote sensing. This geodetic method uses two or more synthetic aperture radar images to generate maps of surface deformation or digital elevation, using differences in the phase of...
- Digital elevation modelDigital elevation modelA digital elevation model is a digital model or 3-D representation of a terrain's surface — commonly for a planet , moon, or asteroid — created from terrain elevation data....
- National Geospatial-Intelligence AgencyNational Geospatial-Intelligence AgencyThe National Geospatial-Intelligence Agency is an agency of the federal government of the United States with the primary mission of collecting, analyzing and distributing geospatial intelligence in support of national security. NGA was formerly known as the National Imagery and Mapping Agency ...
- TerraSAR-XTerraSAR-XTerraSAR-X, a German Earth observation satellite, is a joint venture being carried out under a public-private-partnership between the German Aerospace Center DLR and EADS Astrium GmbH; the exclusive commercial exploitation rights are held by the geo-information service provider Infoterra GmbH....
is a newer satellite with higher resolution - SRTM Water Body DataSRTM Water Body DataThe SRTM Water Body Data is a geographical dataset encoding high-resolution worldwide coastline outlines in a vector format, published by NASA and designed for use in geographic information systems and mapping applications...
External links
- Official NASA SRTM site
- NASA's server with SRTM data tiles - Please read the accompanying documentation
- Maps-For-Free.com Free global relief maps
- GeoSAR, the Testbed for SRTM - Currently owned and operated by Fugro EarthData
- 1-Degree SRTM data tiles in GeoTIFF format - UMD's Global Land Cover Facility
- Void filled SRTM data at CGIAR-CSI and Droppr
- USGS HydroSHEDS - Full resolution SRTM-based DEM for hydrological applications
- Software that can read and process SRTM data: 3dem, GRASS GISGRASS GISGRASS GIS is a free, open source geographical information system capable of handling raster, topological vector, image processing, and graphic data....
, SAGA GISSAGA GISSAGA GIS is a free and open source geographic information system used for editing spatial data. It was originally developed by a small team at the Department of Physical Geography, University of Göttingen, Germany, and is now being maintained and extended by an international developer...
, MapWindow GIS, DG Terrain Viewer/Void Killer, Virtual Terrain Project - Viewfinder Panoramas - Unofficial SRTM data with voids corrected using topographic maps
- Discussion forum for SRTM data users
- Atlogis Meta-Maps: Online-Viewer for relief maps generated from SRTM-Data.
- LatLonToElevation.com Free web application to extract SRTM elevation data given an input file of lat/lon coordinate pairs.
- http://sourceforge.net/projects/srtm-matlab MATLAB-based SRTM reader